Operating mechanism for slidable gates and method of operating slide gate

ABSTRACT

An operating mechanism for slidable gates which are used to control flow of liquid from a bottom-pour vessel, and a flowcontrolling method. The mechanism is particularly useful for controlling teeming of liquid steel from a tundish into a continuous-casting mold. Most slidable gates either fully open or fully close the outlet of a vessel. The present invention enables the outlet to be partially open, whereby the stream discharging therefrom can be throttled. The mechanism includes a main drive means for pushing gates from a ready position to a slow-motion region under the vessel outlet. The slow-motion region of an orifice gate extends at least from a position in which the vessel outlet is partially open to a position in which it is fully open. An opposed auxiliary drive serves to retard movement of a gate as soon as it reaches the slow-motion region. Thereafter, the main drive pushes an orifice gate slowly and under close control to any desired teeming position within the slow-motion region. The mechanism also includes an improved arrangement for conducting gases to the nozzle at the vessel outlet to prevent skulls from forming, and an improved means for attaching a pouring tube to its holder.

1 1 OPERATING MECHANISM FOR SLIDABLE GATES AND METHOD OF OPERATING SLIDEGATE [75] Inventor: Earl P. Shapland, .lr., Champaign,

[73] Assignee: United States Steel Corporation, Pittsburgh, Pa.

[22] Filed: Mar. 1, 1973 [2]] Appl. No.: 337,252

[52] U.S. Cl. 222/504, 222/561 [51] Int. Cl B22d 37/00 [58] Field ofSearch 222/334, 504, 561, DIG. 7

[56] References Cited UNITED STATES PATENTS 3,618,834 11/1971 Shaplancl,Jr. et al. 1. 222/561 3,712,518 1/1973 3,730,401 5/1973 3,752,363 8/1973Fegley et al. 222/63 Primary Examiner-Robert B. Reeves AssistantExaminerDavid A. Scherbel Attorney, Agent, or FirmWalter P. Wood 1 Feb.18, 1975 [57] ABSTRACT An operating mechanism for slidable gates whichare used to control flow of liquid from a bottom-pour vessel, and aflow-controlling method. The mechanism is particularly useful forcontrolling teeming of liquid steel from a tundish into acontinuous-casting mold. Most slidable gates either fully open or fullyclose the outlet of a vessel. The present invention enables the outletto be partially open, whereby the stream discharging therefrom can bethrottled. The mechanism includes a main drive means for pushing gatesfrom a ready position to a slow-motion region under the vessel outlet.The slow-motion region of an orifice gate extends at least from aposition in which the vessel outlet is partially open to a position inwhich it is fully open. An opposed auxiliary drive serves to retardmovement of a gate as soon as it reaches the slowmotion region.Thereafter, the main drive pushes an orifice gate slowly and under closecontrol to any desired teeming position within the slow-motion region.The mechanism also includes an improved arrangement for conducting gasesto the nozzle at the vessel outlet to prevent skulls from forming, andan improved means for attaching a pouring tube to its holder.

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no, m an pil rank 1 OPERATING MECHANISM FOR SLIDABLE GATES AND METHOD OFOPERATING SLIDE GATE This invention relates to an improved operatingmechanism for slidable gates which are used to control flow of liquidfrom a bottom pour vessel, and to an improved flow-controlling method.

Although my invention is not thus limited, my operating mechanism isparticularly useful when applied to a vessel from which liquid metal isteemed into a receiver therebelow, for example, a tundish from whichliquid steel is teemed into a continuous-casting mold. My control methodis particularly useful when applied in the corresponding operation.Reference can be made to an earlier patent of James T. Shapland, US.Pat. No. 3,352,465, of common ownership for a showing of two forms ofslidable gate constructions used heretofore on bottom-pour vessels, andto a number of later patents, also of common ownership, for showings ofmodifications and improvements to the construction shown in the firstShapland patent.

FIGS. l-3 of the Shapland patent show a reciprocating gate, differentportions of which form a closed area and an orifice. The closed area ispositioned under the vessel outlet to prevent flow of liquid from thevessel, and the orifice is positioned thereunder to permit flow. FIGS.4-6 of the patent show slide-through gates, wherein each gate is eithera blank or an orifice gate. A blank gate is positioned under the vesseloutlet to prevent flow, and displaced with an orifice gate to permitflow. With either form, the vessel outlet is either fully open or fullyclosed. There is no provision for teeming through a partially openoutlet, that is, using the gate to throttle the pouring stream. Mostother gate-operating mechanisms with which I am familiar have a similarlack of flexibility.

In certain operations, it would be advantageous to throttle a pouringstream. One example is in continuously casting aluminum-killed steel,where oxygen released from the steel combines with excess aluminum andforms aluminum oxide which deposits around the tundish outlet and gateorifice and restricts flow. If the gate with the orifice could be placedin a throttling position in which the outlet is only partially open atthe beginning of a casting operation, the effective opening could beincreased gradually as the cast progresses to maintain a constantteeming rate and thus compensate for the oxide build-up. Also the gatemight be moved momentarily to a position in which the outlet is fullyopen to flush away the deposit and then returned to a throttlingposition.

An object of my invention is to provide an improved gate-operatingmechanism and an improved flowcontrolling method which enable me tothrottle a stream of liquid as it discharges through the outlet of abottom-pour vessel.

A further object is to provide an improved gateopening mechanism and animproved flow-controlling method which enable me to move an orifice gatequickly from a ready position into a slow-motion region under a vesseloutlet, and thereafter slowly and under close control in eitherdirection to any desired teeming position within the slow-motion region.

A further object is to provide an improved gateoperating mechanism whichenables me to change readily either the blank gate or the orifice gateduring the course of a teeming operation.

A further object is to provide a gate-operating mechanism which affordsthe foregoing advantages and at the same time can be used forpositioning a separate pouring tube beneath the gate.

A further object is to provide an improved means for introducing gas toa permeable plug in a blank gate and avoiding any need for connectingpipes or tubes to movable parts, and also affording automatic gas shutoff when the vessel outlet is opened to begin teeming.

A further object is to provide an improved means for attaching a pouringtube to a holder which can be used in conjunction with a slidable gate.

In the drawings:

FIG. I is a top plan view of my gate-operating mechanism and themounting plate for attaching the mechanism to a bottom-pour vessel;

FIG. 2 is a side elevational view of a portion of a bottom-pour vesselwith my gate-operating mechanism attached; FIG. 3 is a longitudinalsection on line IIIIII of FIG.

FIG. 4 is a cross section on line lV-IV of FIG. 2, but showing a blankgate positioned under the vessel outlet;

FIG. 5 is a cross section on line VV of FIG. 2, but showing a blank gatepositioned under the vessel outlet;

FIG. 6 is a bottom plan view of the mounting plate;

FIG. 7 is an exploded perspective view of the pouring tube and itsholder illustrating my preferred attaching means;

FIG. 8 is a graph comparing the relation between the flow of metal froma tundish and the head of metal therein with the outlet partially open,and the outlet fully open; and

FIG. 9 is a schematic diagram of the hydraulic and pneumatic circuitsembodied in the mechanism.

VESSEL AND MOUNTING PLATE FIGS. 2, 3, 4, and 5 show a portion of aconventional bottom-pour vessel for handling liquid metals, for example,a tundish used to teem metal into a continuouscasting mold. The vesselincludes a metal shell 10, a refractory lining l2, and a refractorypouring nozzle 13 extending through the lining and shell and definingthe outlet. A mounting plate 14 is fixed to the bottom wall of thevessel surrounding the lower portion of the nozzle. Preferably Iinterpose a sheet 15 of heat insulating material, such as asbestos millboard, between the bot-. tom wall and the mounting plate. As best shownin FIG. 6, the mounting plate has horizontal passages 16 and 17. Thepassages 16 communicate with series of nozzles 18 fixed to the undersideof the mounting plate for supplying cooling air to the springs embodiedin my operating mechanism, hereinafter described. The passage 17 has anoutlet port 17a for supplying gas (inert and- /or oxygen) to the vesselnozzle 13 as also hereinafter described. The mounting plate has aplurality of depending lugs 19 for attaching my operating mechanism tothe vessel. The lugs have transverse holes 20.

CONSTRUCTION OF THE GATE OPERATING MECHANISM I construct my operatingmechanism as an assembly which I can install on the mounting plate 14 orremove therefrom as a unit. The mechanism has a fabricated frame 21 onwhich I mount the other parts. As best shown in FIG. 2, this frameincludes a horizontal plate 22, a continuous flange 23 depending fromone side edge of the plate, and vertically spaced upper and lower rails24 and 25 projecting inwardly from the flange. At its opposite sideedge, the plate carries depending flange segments 26, 27, and 28 fromwhich horizontally spaced upper rail segments 29, 30 and 31 respectivelyproject inwardly. Horizontally spaced lower rail segments 32 and 33project inwardly from the flange segments 26 and 28 respectively. Theforegoing parts of the frame are rigidly connected to one another, butpreferably the lower rail 25 and rail segments 32 and 33 and the lowerportions of the flange 23 and flange segments 26 and 28 can be removed.The purpose of the lower rail and rail segments is to support apouring-tube holder 34, hereinafter described. When no pouring tube isused, the parts on which it would have been supported are not needed.Plate 22 has vertical holes 35 and horizontal holes 36 communicatingwith the respective vertical holes. The lugs 19 on the mounting plate 14match the vertical holes and are received therein. I insert pins 37through the aligned horizontal holes 20 and 36 in the lugs 19 and plate22 respectively to hold the operating mechanism on the vessel. Ashereinafter explained in detail, the upper rail 24 and rail segments 29,30 and 31 are adapted to support refractory blank gates 38 and orificegates 39 for movement along a linear path between a ready position, aslowmotion region under the nozzle 13, and a removal position beyond thenozzle.

Plate 22 has-a central opening 41 which receives a stationary refractorytop plate 42 (FIGS. 3, 4 and 5). The latter has the usual orifice 43,which is aligned with the base of the nozzle 13. Since the refractoryplate is exposed directly to liquid metal, it must be replacedfrequently. Replacement is simple, since the top plate is accessiblewhen the frame 21 is removed from the mounting plate 14.

I mount a main fluid-pressure cylinder 46 on frame 21 at one end of thepath of gate movement, and an auxiliary fluid-pressure cylinder 47 atthe other end thereof (FIGS. 1,2 and 3). The main cylinder 46 contains areciprocable piston 48 and a piston rod 49, whichcarries a ram 50 at itsfree end. Similarly, the auxiliary cylinder 47 contains a reciprocablepiston 51 and a piston rod 52, which carries an opposed second ram 53 atits free end. A hydraulic fluid line 54 and a compressed air line 55 areconnected to the back and front ends of the main cylinder 46respectively. Similarly, a hydraulic fluid line 56 and a compressed airline 57 are connected to back and front ends of the auxiliary cylinder47.

At opposite sides of the nozzle 13, the frame 21 carries opposedgate-supporting levers 60 and opposed tube-holder-supporting levers 61which are best shown in FIGS. 4 and 5 respectively. The rails 24 and 25and rail segments 30 are interrupted to accommodate the levers 60 and61, while the levers 61 are slotted to accommodate the levers 60 (FIG.4). The gatesupporting levers 60 are pivotally mounted on crownedwashers 62 carried by bolts 63 which depend from flange 23 and flangesegment 27 at opposite sides of the gate 38 or 39. The flange 23 andflange segment 27 have vertical bores 64 within which I mountcompression springs 65 and plungers 66. The springs act downwardlythrough the plungers against the outboard ends of levers 60, whereby theinboard ends act upwardly against the gate and thus press the gatefirmly against the top plate 42 thereabove. The tube-holder supportinglevers 61 are pivotally mounted on crowned washers 67 carried by bolts68 which depend from flange 23 and flange segment 27 at opposite sidesof the tube holder 34. Springs 69, which are similar to springs 65, actdownwardly through plungers 70 against the outboard ends of levers 61,whereby the inboard ends act upwardly against the tube holder and thenpress the tube holder firmly against the gate 38 or 39 thereabove. Thebores which receive the springs lie directly under the respectivenozzles 18 in the mounting plate 14 to admit cooling air to the springs.

OPERATION OF THE GATE-OPERATING MECHANISM Before filling the vessel withmetal or other liquid, I position a blank gate 38 under the stationarytop plate 42, where it is supported on the inboard arms of thegate-supporting levers 60. The ram 50, operated by the main cylinder 46,is fully retracted. The back end of the auxiliary cylinder 47 containshydraulic fluid, whereby the second ram 53 is extended into abuttingrelation with the end of the blank gate 38. I insert an orifice gate 39sideways through the space between the upper flange segments 26 and 27into a ready position, where it rests on the rail 24 and on railsegments 29 and 30. The orifice gate 39 has an orifice 73 of the samediam eter as the orifice 43 in the top plate 42. The ends of the gates38 and 39 approximately abut.

When I wish to commence teeming, I introduce hydraulic fluid to the backend of the main cylinder 46 via the line 54. Ram 50 is driven toward thenozzle 13 and thus pushes the orifice gate 39 toward the nozzle anddisplaces the blank gate 38 from the gate-supporting levers 60 toward aremoval position beyond the nozzle. The blank gate acts against ram 53and pushes the piston 51 into a retracted position within the auxiliarycylinder 47. The back end of the piston 51 carries a cylindrical plug 74(FIG. 3). The back wall of cylinder 47 has a bore 75, which is adaptedto receive plug 74, and with which the hydraulic line 56 communicates.The back wall also has a restricted L-shaped passage 76 which affordsthe only communication between the interior of the cylinder and the bore75 when plug 74 is received within the bore. A screw 77, which isthreadedly engaged with the cylinder wall, controls the effectivecross-sectional area of passage 76. Thus the plug 74, bore 75, andpassage 76 form a dashpot. I proportion the parts so that the plug firstenters the bore when the orifice gate 39 reaches a slow-motion region inwhich it is supported on the gate-supporting levers 60 and its orifice73 is nearing or partially under the nozzle 13. The slow-motion regionof an orifice gate extends at least from a position of the gate in whichthe nozzle is partially open, as shown in FIG. 3, to a position in whichthe nozzle is fully open. Until the plug enters the bore, hydraulicfluid discharges freely from the auxiliary cylinder, whereby the partsmove rapidly until the gate reaches the slow-motion region. As soon asthe plug enters the bore, hydraulic fluid can escape from the auxiliarycylinder only via the restricted passage 76, whereupon the parts moveslowly and under close control in either direction into any desiredteeming position within the slow-motion region.

While the teeming operation takes place, the upper rail segments 30 and31 support the blank gate 38 in its removal position, and thegate-supporting levers 60 support the orifice gate 39, as alreadystated. If I wish to remove the blank gate and replace it with another,I introduce air under pressure to the front end of the auxiliarycylinder 47 via line 57. Piston 52 is driven into a more retractedposition, whereupon I can remove the blank gate sideways through thespace between the flange segments 30 and 31, and insert another in itsplace. If I wish to stop pouring, I introduce hydraulic fluid to theback end of the auxiliary cylinder 47 and thus push the blank gate 38from its removal position back under the orifice 43, slowly at firstuntil plug 74 clears the bore 75 and then rapidly. IfI wish to changeorifice gates, I first remove the blank gate by the procedure alreadydescribed, whereafter I introduce air to the front end of the maincylinder 46 via the line 55 and thus drive the piston 48 and ram 50 intoa retracted position. I insert a new orifice gate into the readyposition and next operate cylinder 46 to push the new gate into theslow-motion region on the gate-supporting levers 60, displacing the oldorifice gate into its removal position. Alternatively, I may introducehydraulic fluid to the back end of the auxiliary cylinder 47 and drivethe blank gate back under the nozzle and the old orifice gate back tothe ready position, from which I remove it sideways. I can then insert anew orifice gate into the ready position and proceed as originallydescribed.

FIG. 8 is a graph which shows the relation between the flow rate andhead of steel in a tundish (A) with the gate orifice 73 in an initialthrottling position at the beginning of the slowmotion region, and (b)with the gate orifice in its fully open position. In this instance, theinitial throttling position is with the circumference of the gateorifice 73 lying on the center of the orifice 42 in the top plate 41,that is, the effective area of the opening is about 40 percent of thearea at the fully open position. The abscissae of the graph representthe flow rate and the ordinates the head. In each instance, the flowrate is directly proportional to the head. With a given size of orificeand a given initial throttling position, I can produce a relationanywhere between the lines (A) and (B) of the graph.

HYDRAULIC AND PNEUMATIC CIRCUITS FIG. 9 is a simplified diagram of thehydraulic and pneumatic circuits embodied in mymechanism. The hydrauliccircuit includes a tank 80 which contains hydraulic fluid. A feed line81 extends from the tank to a pump 82 and thence to-an inlet port of afour-way valve 83. A return line 84 extends from an outlet port of thevalve back to the tank. The aforementioned hydraulic lines 54 and 56extend from this valve to the main and auxiliary cylinder 46 and 47respectively. The pneumatic circuit includes a compressed air tank 85. Afeed line 86 extends from tank 85 to an inlet port of another four-wayvalve 87, which has an exhaust 88. The aforementioned air lines 55 and57 extend from the latter valve to the main and auxiliary cylinders 46and 47 respectively. FIG. 9 shows the valves 83 and 87 in their neutralpositions. When I wish to introduce hydraulic fluid to cylinder 46 or47, I shift the movable element of valve 83 left or right respectively.Similarly, I shift the movable element of valve 87 to introduce air toeither cylinder. The circuit may include various refinements, not shown,such as filters, heaters, and accumulators.

INTRODUCTION OF GAS TO NOZZLE The blank gate 38 illustrated has agas-permeable plug 91 which is aligned with orifice 43 when the blankgate is positioned to close the vessel outlet. As known in the art, Iintroduce gas to the base of nozzle 13 through the permeable plug toprevent skulls from forming and blocking the nozzle. Preferably, Iintroduce an inert gas, usually argon, to stir the metal in the vesseluntil a few seconds before I am ready to commence teeming. At thatpoint, I introduce a brief burst of oxygen to burn away any skull whichmay have formed in the nozzle bore. The inclusion of a permeable plug ofcourse is optional, but when I include it, I prefer to conduct gas tothe plug through a novel arrangement of passages, which are best shownin FIGS. 1 and 5 and which I shall now describe.

As already mentioned, the mounting plate 14 has a passage 17 and anoutlet port 170. The top plate 42 has a horizontal passage 92 and inletand outlet ports 92a and 92b communicating with this passage andextending through the top and bottom faces respectively. The blank gate38 has a horizontal passage 93, an inlet port 93a communicating withthis passage and extending through the top face, and a circular passage94 communicating with passage 93 and surrounding the permeable plug 91.When the parts are assembled, the outlet port 17a in the mounting plateand the inlet port 92a in the top plate 42 are aligned. Preferably, Iinsert a sealing ring 95 between the top plate and mounting plate at thejuncture of the outlet and inlet ports. When the blank gate 38 isproperly positioned under the nozzle 13, the inlet port 93a in the gateand the outlet port 92b in the top plate are aligned. I connect a gasline 96 to either end of passage 17 in the mounting plate, whereby gasmay flow through passages 17, 92, 93 and 94 to the permeable plug 91.The other end of passage 17 of course is plugged.

My novel arrangement of passages eliminates need for connecting a pipeor tube to a movable part of the mechanism to conduct gas to the plug,as has been the practice in the prior art. A further advantage is thatthe gas is immediately and automatically shut off whenever the blankgate is displaced from the nozzle. It should be pointed out that mynovel arrangement of passages has general utility in gate-operatingmechanisms which embody a mounting plate, a top plate, and a permeableplug in the slidable gate. Its use is not confined to the specificmechanism described herein.

POURING TUBE CONSTRUCTION AND OPERATION If I use a pouring tube, 1assemble the tube 98 on its aforementioned holder 34. As best shown inFIg. 7, the holder 34 is formed of a flat rectangular refractory block99 and a metal frame 100 covering the side and end edges and bottom ofthe block. The frame is fixed to the block with 'a layer of mortar 101.The underside of the frame has a depending skirt 102 which receives theupper end of tube 98. The skirt has four symmetrically arranged slots103. The upper portion of the tube has a surrounding metal band 104 andis grooved as indicated at 105. I insert a U-shaped wire clip 106through the slots 103 and grooves to fix the pouring tube to the holder.The block 99 has a central orifree 107 aligned with the tube bore. Thegrooves 105 preferably extend through only relatively small arcs,whereby the tube is positioned automatically always in the sameorientation with respect to the holder when the two parts are assembled.This is an important advantage where the tube has outlets 108 in itsside walls, since it assures that these outlets are oriented properlywith respect to a continuous casting mold. lf side outlets are not used,groove 105 may be continuous around the tube circumference. When eitherthe holder or tube requires replacement, it can be replaced withoutreplacing the other.

When I install the holder 34 and pouring tube 98 in the mechanism, 1insert the holder sideways through the space between the lower railsegment 32 and the holder-supporting levers 61, where it is in a readyposition resting on the lower rail 25 and rail segment 32. Rams 50 and53 have depending flanges 109 and 110 respectively adapted to abutopposite ends of holder 34. Initially I operate the main cylinder 46 toextend ram 50 and push the holder into a position in which its orifice107 is aligned with nozzle 13. Preferably I insert a U-shaped stop 112through appropriately placed holes in the lower rail 25 to retain theholder and tube exactly in this position. When I replace a tube holderand tube, 1 insert a replacement holder into the ready position the sameas before, and operate cylinder 46 to push the replacement holder ontothe holdersupporting levers 61, where it displaces the old onto thelower rail 25 and rail segment 33. I can remove the holder sidewaysthrough the space between the rail segment 33 and the levers 61.

From the foregoing description, it is seen that my invention affords asimple method and mechanism for operating slidable gates which controlflow of liquid from a bottom-pour vessel and for using the orifice gateto throttle the pouring stream. The invention enables gates or pouringtubes to be removed and replaced readily at any time. Another feature isthat the pouring tube is removably attached to its holder, yet alwaysproperly oriented.

I claim:

1. An operating mechanism for slidable gates which are used to controlflow of liquid from a bottom-pour vessel, said mechanism comprising aframe for attachment to the bottom of the vessel, gate-supporting meanson said frame for slidably supporting blank and orifice gates formovement between a ready position, a slow-motion region under the vesseloutlet, and a removal position beyond said slow-motion region, theslow-motion region of an orifice gate extending at least from a positionof the gate in which the vessel outlet is partially open to a positionin which it is fully open, and main and auxiliary drive means carried bysaid frame at opposite ends of the path of gate movement, said maindrive means being adapted to push a gate from said ready position intosaid slow-motion region and to displace a gate already in saidslow-motion region into said removal position, said auxiliary drivemeans including means for retarding the rate of movement of gates asthey reach said slow-motion region, which lastnamed means permits anorifice gate to move rapidly from said ready position to saidslow-motion region and thereafter slowly and under close control ineither direction to any teeming position within said slow-motion region.

2. A mechanism as defined in claim 1 comprising in addition means onsaid frame spaced below said gatesupporting means for supporting apouring tube.

3. A mechanism as defined in claim 2 in which the means for supportingthe pouring tube enables said main drive means to push a replacementpouring tube from a ready position into a position aligned with thevessel outlet, and to displace an old pouring tube from alignment withthe outlet into a position from which it can be removed sideways.

4. A mechanism as defined in claim 1 in which said main and auxiliarydrive means include fluid pressure cylinders and pistons mounted atopposite ends of said frame, and opposed rams operated by said pistons.

5. A mechanism as defined in claim 4 in which said retardingmeansinclude a dashpot within the cylinder of said auxiliary drive means.

6. The combination, with a bottom-pour vessel having a nozzle in itsbottom wall and blank and orifice gates for controlling flow of liquidthrough said nozzle, of an operating mechanism attached to the bottomwall of said vessel for supporting and positioning said gates, saidmechanism being constructed as defined in claim 1.

7. A combination as defined in claim 6 further comprising a pouring tubecarried by said mechanism below said gates.

8. A combination as defined in claim 6 in which said mechanism forms anassembly which can be removed as a unit from said vessel, andre-attached thereto.

9. In an operating mechanism for slidable gates which are used tocontrol flow of liquid from a bottom-pour vessel, which mechanismcomprises:

a frame for attachment to the bottom of the vessel and including a plateand rails dependently supported from said plate;

opposed gate-supporting levers pivoted to said frame, said rails beinginterrupted to accommodate said levers; and

a main fluid pressure cylinder and piston and a ram operated therebymounted at one end of said frame;

the improvement which comprises:

an auxiliary cylinder and piston and an opposed second ram operatedthereby mounted at the other end of said frame;

said rails being adapted to support blank and orifice gates for movementbetween a ready position adjacent said first-named ram, a slow-motionregion on said levers under the vessel outlet, and a removal positionadjacent said second ram;

the slow-motion region of an orifice gate extending at least from aposition of the gate in which the vessel outlet is partially open to aposition in which it is fully open;

said first-named ram being adapted to push a gate from said readyposition into said slow-motion region, and to displace a gate from thelatter region to said removal position with said second ram in abuttingrelation with the displaced gate;

and means in said auxiliary cylinder for retarding the rate of movementof the gates as they reach said slow-motion region, whereby an orificegate moves rapidly from said ready position to said slowmotion regionand thereafter slowly and under close control in either direction to anyteeming position within said slow-motion region.

10. A mechanism as defined in claim 9 in which the gates can be insertedsideways into their ready position and removed sideways from theirremoval position.

11. A mechanism as defined in claim 9 in which said frame includes inaddition rails spaced below said firstnamed rails for supporting apouring tube, said mechanism further comprising opposed tube-supportinglevers below said gate-supporting levers, said secondnamed rails beinginterrupted to accommodate said tube-supporting levers, and means onsaid first-named ram for pushing a pouring tube from said second railsto said tube-supporting levers.

12. A mechanism as defined in claim 9 in which said retarding meansincludes a dashpot within said auxiliary cylinder, said check valvebecoming operable when a gate reaches a slow-motion region.

13. The combination, with a bottom-pour vessel having a nozzle in itsbottom wall, a mounting plate fixed to the bottom wall and surroundingsaid nozzle, a top plate under said mounting plate, and blank andorifice gates for controlling flow of liquid through said nozzle, of anoperating mechanism for supporting and positioning said gates, saidmechanism being removably 'attached to said mounting plate andconstructed as defined in claim 9.

14. A combination as defined in claim 13 in which said mounting platecarries a plurality of depending lugs, and the frame of said mechanismincludes a plate having holes matching and receiving said lugs, and pinsfixing said frame to said lugs.

15. A method of controlling flow of liquid from a bottom-pour vessel,said method comprising positioning a blank gate under the vessel outlet,hydraulically displacing the blank gate with an orifice gate, and duringthe displacing step moving the orifice gate rapidly from a readyposition to a slow-motion region under the outlet and thereafter slowlymoving the orifice gate under close control to a teeming position withinthe slowmotion region by retarding the gates with a dashpot in thehydraulic circuit, said slow-motion region of an orifice gate extendingat least from a position of the gate in which the vessel outlet ispartially open to a position in which it is fully open.

16. In an operating mechanism for slidable gates which are used tocontrol flow of liquid from bottompour vessel, said mechanismcomprising:

a frame for attachment to a vessel;

gate supporting means on said frame for slidably supporting blank andorifice gates for movement between a ready position, a position underthe vessel outlet and for removal; and

drive means for moving said gates;

the improvement in which:

said orifice gate is movable rapidly from said ready position to aslow-motion region under the vessel outlet extending at least between aposition in which the outlet is partially open and a position in whichit is fully open; and

said drive means is plural speed, and has means for moving said orificegate at a first rapid speed from said ready position to said slow-motionregion and means for moving said orifice gate at a second slow speedthrough said slow-motion region.

1. An operating mechanism for slidable gates which are used to controlflow of liquid from a bottom-pour vessel, said mechanism comprising aframe for attachment to the bottom of the vessel, gate-supporting meanson said frame for slidably supporting blank and orifice gates formovement between a ready position, a slowmotion region under the vesseloutlet, and a removal position beyond said slow-motion region, theslow-motion region of an orifice gate extending at least from a positionof the gate in which the vessel outlet is partially open to a positionin which it is fully open, and main and auxiliary drive means carried bysaid frame at opposite ends of the path of gate movement, said maindrive means being adapted to push a gate from said ready position intosaid slow-motion region and to displace a gate already in saidslow-motion region into said removal position, said auxiliary drivemeans including means for retarding the rate of movement of gates asthey reach said slow-motion region, which last-named means permits anorifice gate to move rapidly from said ready position to saidslow-motion region and thereafter slowly and under close control ineither direction to any teeming position within said slow-motion region.2. A mechanism as defined in claim 1 comprising in addition means onsaid frame spaced below said gate-supporting means for supporting apouring tube.
 3. A mechanism as defined in claim 2 in which the meansfor supporting the pouring tube enables said main drive means to push areplacement pouring tube from a ready position into a position alignedwith the vessel outlet, and to displace an old pouring tube fromalignment with the outlet into a position from which it can be removedsideways.
 4. A mechanism as defined in claim 1 in which said main andauxiliary drive means include fluid pressure cylinders and pistonsmounted at opposite ends of said frame, and opposed rams operated bysaid pistons.
 5. A mechanism as defined in claim 4 in which saidretarding means include a dashpot within the cylinder of said auxiliarydrive means.
 6. The combination, with a bottom-pour vessel having anozzle in its bottom wall and blank and orifice gates for controllingflow of liquid through said nozzle, of an operating mechanism attachedto the bottom wall of said vessel for supporting and positioning saidgates, said mechanism being constructed as defined in claim
 7. Acombination as defined in claim 6 further comprising a pouring tubecarried by said mechanism below said gates.
 8. A combination as definedin claim 6 in which said mechanism forms an assembly which can beremoved as a unit from said vessel, and re-attached thereto.
 9. In anoperating mechanism for slidable gates which are used to control flow ofliquid from a bottom-pour vessel, which mechanism comprises: a frame forattachment to the bottom of the vessel and including a plate and railsdependently supported from said plate; opposed gate-supporting leverspivoted to said frame, said rails being interrupted to accommodate saidlevers; and a main fluid pressure cylinder and piston and a ram operatedthereby mounted at one end of said frame; the improvement whichcomprises: an auxiliary cylinder and piston and an opposed second ramoperated thereby mounted at the other end of said frame; said railsbeing adapted to support blank and orifice gates for movement between aready position adjacent said first-named ram, a slow-motion region onsaid levers under the vessel outlet, and a removal position adjacentsaid second ram; the slow-motion region of an orifice gate extending atleast from a position of the gate in which the vessel outlet ispartially open to a position in which it is fUlly open; said first-namedram being adapted to push a gate from said ready position into saidslow-motion region, and to displace a gate from the latter region tosaid removal position with said second ram in abutting relation with thedisplaced gate; and means in said auxiliary cylinder for retarding therate of movement of the gates as they reach said slow-motion region,whereby an orifice gate moves rapidly from said ready position to saidslow-motion region and thereafter slowly and under close control ineither direction to any teeming position within said slow-motion region.10. A mechanism as defined in claim 9 in which the gates can be insertedsideways into their ready position and removed sideways from theirremoval position.
 11. A mechanism as defined in claim 9 in which saidframe includes in addition rails spaced below said first-named rails forsupporting a pouring tube, said mechanism further comprising opposedtube-supporting levers below said gate-supporting levers, saidsecond-named rails being interrupted to accommodate said tube-supportinglevers, and means on said first-named ram for pushing a pouring tubefrom said second rails to said tube-supporting levers.
 12. A mechanismas defined in claim 9 in which said retarding means includes a dashpotwithin said auxiliary cylinder, said check valve becoming operable whena gate reaches a slow-motion region.
 13. The combination, with abottom-pour vessel having a nozzle in its bottom wall, a mounting platefixed to the bottom wall and surrounding said nozzle, a top plate undersaid mounting plate, and blank and orifice gates for controlling flow ofliquid through said nozzle, of an operating mechanism for supporting andpositioning said gates, said mechanism being removably attached to saidmounting plate and constructed as defined in claim
 9. 14. A combinationas defined in claim 13 in which said mounting plate carries a pluralityof depending lugs, and the frame of said mechanism includes a platehaving holes matching and receiving said lugs, and pins fixing saidframe to said lugs.
 15. A method of controlling flow of liquid from abottom-pour vessel, said method comprising positioning a blank gateunder the vessel outlet, hydraulically displacing the blank gate with anorifice gate, and during the displacing step moving the orifice gaterapidly from a ready position to a slow-motion region under the outletand thereafter slowly moving the orifice gate under close control to ateeming position within the slow-motion region by retarding the gateswith a dashpot in the hydraulic circuit, said slow-motion region of anorifice gate extending at least from a position of the gate in which thevessel outlet is partially open to a position in which it is fully open.16. In an operating mechanism for slidable gates which are used tocontrol flow of liquid from bottom-pour vessel, said mechanismcomprising: a frame for attachment to a vessel; gate supporting means onsaid frame for slidably supporting blank and orifice gates for movementbetween a ready position, a position under the vessel outlet and forremoval; and drive means for moving said gates; the improvement inwhich: said orifice gate is movable rapidly from said ready position toa slow-motion region under the vessel outlet extending at least betweena position in which the outlet is partially open and a position in whichit is fully open; and said drive means is plural speed, and has meansfor moving said orifice gate at a first rapid speed from said readyposition to said slow-motion region and means for moving said orificegate at a second slow speed through said slow-motion region.